This will be used to persist CDC streams generation timestamp
proposed by a joining node in case the node crashes or restarts,
similarly to the way tokens are persisted.
The get_saved_cdc_streams_timestamp method retrieves the generation
timestamp from the system table. It will be used by a restarting
node.
The update_cdc_streams_timestamp method saves CDC stream
generation timestamp of the calling node in the system table.
A joining node will persist the timestamp before it proposes it to other
nodes.
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